Sil E is a low molecular weight 123 amino acid protein that binds about four silver ions and pCoE is a very similar protein that binds about four copper ions. Sil E is an extracellular periplasmic Ag(I)-binding protein involved in Ag(I) resistance and only resistance to Ag(I) and pCoE is thought to have a similar function for Cu(I). These proteins have ten histidimes, which are thought to provide donor atoms for Ag(I) and Cu(I). We have titrated these proteins with Cu(II) and found that about four Cu(II)=s with the same ESR signal are also bound to both of these proteins. Low frequency, S-band, spectra will be obtained in the future to determine the number of nitrogen bound to Cu(II).